This invention relates, generally, to bus duct apparatus for use with plug-in units and more particularly to a grounding spring to ground the plug-in unit to the bus duct before the phase stabs of the plug-in unit make contact with the bus bars of the duct.
Most duct assemblies when installed with associated accessories such as plug-in power take-off units have generally required a make-shift operation to ensure proper enclosure to enclosure grounding. However, recent requirements by testing institutions such as Underwriter Laboratories with reference to Section 857, and the National Electrical Code of 1981, Article 250-99, mandate more reliable grounding between plug-in units and the associated bus duct. This has led to the requirement that the housing of the plug-in unit be grounded to the bus duct housing before the phase stabs contained in the plug-in unit make contact with the bus bars contained in the bus duct and that upon the removal of a plug-in unit, this ground between the plug-in unit and the bus duct housing be broken only after the phase stabs break contact with the bus bars.
It would be advantageous to provide a means whereby the bus duct enclosure is grounded to the plug-in unit enclosure before the phase stabs are energized by the bus bars and break ground only after the phase stabs are deenergized while still utilizing existing plug-in units and bus duct housings. Also advantageous would be a means of accomplishing such grounding in a relatively inexpensive manner which is easy to manufacture and install.